(Not OP) For me on Android Firefox the topic menu takes up the whole screen, doesn't scroll, and doesn't hide. On Chrome it seems to work.
Happens to me too =/
Firefox on Android.
OP here — works for me on mobile Safari
2021 and developers are still responding to support issues with "works on my machine!"
Ha ha! I'm not a dev any more, but old habits die hard, I guess. My comment was, in fact, to confirm for anyone who wanted to access with mobile Safari but who hadn't yet, that it indeed would work fine.